Because of alumina's many advantages, and more particularly, because it is highly inert to oxidizing atmospheres, has excellent acid resistance and alkali resistance and is inexpensive, alumina finds wide application as a common structural material. Furthermore, alumina has been used for purposes having more demanding requirements. In general, alumina having a coarser sintered structure has better grindability and polishability, however, the strength of the resulting alumina material is lowered. On the other hand, alumina having a finer sintered structure provides a higher strength alumina material, however, the grindability and polishability of the alumina is lowered. Thus, it is generally difficult to provide alumina having both the desired grindability or polishability and strength at the same time.
High purity alumina having an alumina content of not less than 98% by weight, particularly not less than 99% by weight, has high chemical inertness and rigidity and excellent electrical insulating properties. Thus, high purity alumina is often used for making parts for semiconductor fabrication equipment. In more detail, high purity alumina often finds application as a jig for polishing, chemical treatment and plasma treatment of silicon wafers. Such a jig requires high dimensional accuracy. In general, however, ceramics shrink at the sintering step. Accordingly, if used as a part requiring high dimensional accuracy such as the foregoing jig, ceramics which have been sintered must first be subjected to grinding.
In order to grind ceramics, a diamond grinding wheel is generally used. In more detail, ceramics are subjected to cylindrical, surface, inner diameter, profile or creep feed grinding using a wet process. However, a diamond grinding wheel is very expensive. Furthermore, in the case of ceramics, cracking during working and the roughness of the finished surface have a greater effect on the properties of the resulting product as compared with metal. Thus, ceramics cannot be subjected to heavy-duty grinding. Accordingly, the grinding of ceramics takes a prolonged period of time. When combined with the expense of the diamond grinding wheel, the grinding step incurs a very high cost. As a result, the resulting jig or other products are made more expensive.